1. Field of the Invention
The present invention relates to a semiconductor device including a complementary logic circuit and a driving method thereof.
2. Description of the Related Art
In recent years, a metal oxide showing semiconductor characteristics, which is called an oxide semiconductor, has attracted attention as a novel semiconductor material having high mobility which can be obtained by polysilicon and having uniform element characteristics which can be obtained by amorphous silicon. The metal oxide is used for various applications. For example, indium oxide is a well-known metal oxide and used as a material of a transparent electrode included in a liquid crystal display device or the like. Examples of such metal oxides having semiconductor characteristics include tungsten oxide, tin oxide, indium oxide, and zinc oxide. Transistors in each of which a channel formation region is formed using such a metal oxide having semiconductor characteristics have been known (Patent Documents 1 and 2).